We live in the information-intensive society. However, our information handling capacity is limited. Conventionally, most information presentation systems rely on visual or audio means. Such information presentation relying on visual or audio means has a problem that, since visual or audio information is intensively provided, the user's attention is excessively focused to that information. Furthermore, when a person receives a visual or audio stimulus, the person's brain has to interpret the stimulus before reflecting it in the person's action. Therefore, there is also a problem that it takes relatively long for the person to act in response to reception of the information.
To solve such problems, as an information presentation channel other than the visual or audio channel, a force sense channel, such as sense of a force exerted on a hand, is being developed.
Conventional researches on the force sense can be classified into two types: the grounded type and the ungrounded type. The grounded type involves a supporting point of a reaction force of a force to be generated or a point of application of force fixed outside or on a human body. The ungrounded type does not involve such a supporting point or a point of application of force (see the non-patent literature 1 and the patent literature 1, for example).
However, conventional force sense generating methods have a problem that those methods are difficult to apply to portable devices, such as mobile devices and wearable computers.
For example, the grounded type that involves a supporting point or a point of application of force fixed outside is difficult to apply to a mobile device or wearable computer, which is intended to be carried arbitrarily. In the case of the grounded type that involves a supporting point or a point of application of force fixed on a site of the body of a person other than the point of action of force, the reaction force of the sensed force is also exerted on the body of the person, and as a result, it is difficult to provide accurate information about the direction of the force. The art described in the patent literature 1 “IMPULSIVE FORCE GENERATOR, ITS CONTROLLER, CONTROLLING METHOD AND PROGRAM” is intended to solve the problem described above by using the reaction of an abrupt moment force. However, according to this art, only the force sense of an impulsive force can be provided, and it is difficult to provide a temporally stable force sense.
The inventor of the present application has proposed a method of making a person sense a temporally stable force without a supporting point of a reaction force or a point of application of force (see Japanese Patent Application Laid Open No. 2006-065665, which had not yet been published at the priority date of the present application). According to this method, a rotational motive force is transmitted to a link mechanism or the like to generate an acceleration that substantially varies in absolute value depending on whether the acceleration is a positive acceleration or a negative acceleration.    Non-patent literature 1: Naoyuki Kakehi, Hiroaki Yano, Makoto Saito, Tetsuro Ogi, Michitaka Hirose, “Development and Evaluation of Force Display Device HapticGEAR in Immersive Virtual Space”, Journal of Virtual Reality Society of Japan, VOL. 5, No. 4, pp. 1113-1120, 2000    Patent literature 1: Japanese Patent Application Laid-Open No. 2002-346225